This invention relates to a fusible link wire, and more particularly, to a fusible link wire especially adaptable for use as a low tension cable found in automotive electrical harnesses.
Fusible link wire is an overcurrent protection device for an electrical circuit that utilizes a conductor which is generally two to four AWG wire sizes smaller or has a higher relative resistance than the other conductors in the electrical circuit. Fusible link wires commonly comprise a central electrical conductor, such as stranded copper, tin-coated copper, brass, copper-nickel alloys or other similar metals, surrounded by a thermosetting electrical insulation typically made from chlorosulfonated polyethylene, having relatively good insulating properties and resistance to heat and the adverse chemical environment present in the vicinity of an automobile engine.
In operation, when a conducting electrical circuit having a fusible link wire is placed under extreme overload conditions, the temperature of the smaller fusible link conductor increases more rapidly than the conductors of the other wires in the circuit. This relatively rapid temperature rise continues until the conductor melts and opens the conducting circuit. Previous prior art fusible link wires, however, have been found to be unsatisfactory. The rapid heating of the conductor and the insulation typically produces inflammable gasses which become trapped along the surface of the conductor and can ignite at the high temperatures encountered during the overload conditions. Furthermore, when the insulation degrades, or otherwise breaks down and fails, an exposed, energized conductor or energized-conductor end can result, creating an unacceptable operating condition.
Consequently, a need exists for a fusible link wire comprising a conductor having excellent electrical conductivity characteristics and a high temperature electrical insulation which is abrasion and chemical resistant, high temperature cut-through resistant, and resistant to aging. Furthermore, the insulation should be highly resistant to physical breakdown, flame retardant and permit the rapid dispersion of gasses.